EP-A-0 421 127 discloses an apparatus for treating printed circuit boards, whereby the individual printed circuit boards are continuously conducted through successively arranged treatment baths in a vertically suspended attitude on a horizontal transport path. The transport of the printed circuit boards through the treatment baths accommodated in the treatment cells occurs via clamps arranged at endlessly circulating drives, and these clamps also simultaneously assume the cathodic contacting of the printed circuit boards in the case of a galvanic treatment. Vertical slots for the passage of the printed circuit boards are situated in the end walls of the treatment cells, whereby seals fashioned as brush seals or stripper brush seals are provided in the passage region. The individual treatment cells are arranged in collecting troughs from which the collected bath fluid is continuously returned into the allocated treatment cells with the assistance of corresponding pumps. Here, too, a constant level is enabled in the individual treatment cells due to the continuous return of the bath fluid.
U.S. Pat. No. 4,401,522 discloses a similarly constructed apparatus for the electrolytic treatment of printed circuit boards wherein vertically arranged roller pairs as seals are allocated to the vertical slots in the end walls of the treatment cells. The rollers of these roller pairs, composed of elastic material, are resiliently pressed against one another and are driven at a rotational speed matched to the transport speed of the traversing printed circuit boards.
In another apparatus for the treatment of plate-shaped workpieces, particularly printed circuit boards, disclosed by EP-B-0 760 023, rods or tubes, loosely arranged in pairs in a vertical alignment in the treatment bath, are allocated to the vertical slots as seals. Due to their loose arrangement in the treatment bath, these rods or tubes are pressed against one another by the fluid pressure or against the respectively traversing workpiece and against the allocated end wall of the treatment cell. The seal of the vertical slots here is thus practically automatically effected by the pressure of the bath fluid.
The above-described sealing principle with seals loosely arranged in the treatment bath has proven excellent in the treatment of workpieces or, respectively, printed circuit boards having plate thicknesses of more than 0.25 mm. Given workpieces having plates thicknesses of up to 0.25 mm, particularly given thin, non-rigid printed circuit boards, however, deformations of the workpieces occur at the admission side upon entry into the treatment cell. These deformations are to be attributed to the high fluid pressure in the lower region of the treatment cells as a result whereof the seals are pressed more greatly against one another in the lower region and make the entry of the workpieces into the treatment cell more difficult.
EP-A-0 289 195 discloses an apparatus for treating plate-shaped workpieces, particularly printed circuit boards, in a vacuum chamber, whereby the workpieces are continuously transported into the vacuum chamber in a vertical attitude on a horizontal transport path via a first seal, a first lock chamber and a second seal and in turn depart from the vacuum chamber via a third seal, a second lock chamber and a fourth seal. Within the vacuum chamber, the workpieces are treated, for example, by sputtering, plasma etching, vapor-deposition or CVD deposition. The first and the fourth seal are respectively composed of two pipes or rods that are arranged in recesses at both sides of the transport path so that they lie against the traversing workpieces. The vertically directed seals are thereby respectively rotatably seated in a head plate and a bottom plate, whereby the vertical guidance of the workpieces ensues with a lower guide rail projecting from the bottom plate and an upper guide rail resiliently seated in the head plate. A roller pair, which is arranged at the admission side spaced from the first seal, is provided for the transport of the workpieces by inserting a workpiece into a vertical slot of the supporting housing for the first seal and, thus, pushing all workpieces lying against one another through the apparatus.
The invention is based on the problem of making the seal system in the apparatus disclosed by EP-B-0 760 023 for the treatment of plate-shaped workpieces more suitable such that a treatment of thin workpieces is also enabled.
The invention is based on the perception that a guidance and stiffening of thin work pieces is effected by a roller pair arranged immediately preceding the seats at the admission side and this then enables an unproblemmatical entry into the seals and into the treatment bath. It is thereby to be emphasized that as a result of seals arranged loosely in the treatment bath and guide rollers, both thin as well as thick work pieces can be treated.
The development which provides an additional pair of vertically arranged rollers at the discharge side of the treatment cell or bath, enables a reliable discharge of thin work pieces from the treatment bath as needed. A bending of thin work pieces upon discharge from the treatment bath, however, need only be feared in exceptional cases, since the liquid pressure onto the work pieces here corresponds to the pressure on the seals.
The development of driving the rollers facilitates the entry of the work pieces into a roller pair to a considerable extent. Even thinner work pieces than given rollers that are not driven can thus be handled.
The development of using the transport means or device to drive the rollers enables a drive of the rollers with minimum outlay. Moreover, a matching of the roller speed to the transport speed of the traversing workpieces is always assured given a drive of the rollers by the transport means. A frictional drive of the rollers by the transport means is preferred, since it is extremely rugged and can be realized with little outlay. Means for a resilient placement of one of the rollers of each pair enables an automatic adaptation of the roller guidance to the thickness of the work pieces to be respectively treated.